With no evidence of sabotage in the New York City crash, the focus shifts to the plane and its pilots

Composite parts, however, can be weakened by manufacturing flaws, by water seeping in between layers or by direct impact. And the NTSB won't yet exclude sabotage as a possible cause of the crash. Although most security experts say it would be extremely difficult for someone to loosen screws on the tail assembly or damage it in some way, investigators haven't ruled out those possibilities. "People are acting almost as if this airplane was randomly designed," says Paul Czysz, a professor at Parks College of Engineering and Aviation at St. Louis University. "It was fatigue tested, and I'm sorry, but it just doesn't come apart like that."

So as the NTSB continues its investigation, the flying public is left with several possible causes of the crash of Flight 587, none of them particularly reassuring. Flyers will do well to keep in mind more comforting data: 610 million passengers boarded 9 million domestic commercial flights last year, and all but 87 made it home. That's a far lower accident rate than the one for Americans who drive to their holiday destinations.